This invention relates to a method of detecting an abnormality in an electromagnetic valve current controller. More particularly, the invention relates to a method of detecting an abnormality in the current controller of an electromagnetic valve used in controlling the amount of supplementary air supplied to an internal combustion engine to control the idling operation thereof.
Duty ratio control-type electromagnetic valves have been in general use as valves for controlling the amount of supplementary air supplied to an internal combustion engine in order to control its idling operation. Recently, however, a proportional control-type electromagnetic valve (hereafter referred to as a "proportional electromagnetic valve") which features more reliable control has come into use for this purpose. A proportional electromagnetic valve ordinarily is of the normally closed type and includes a valve body capable of continuously changing the opening area of the passageway in which the valve is installed, a spring for biasing the valve body in the closing direction, and an electromagnetic solenoid which, when energized, moves the valve body in the opening direction against the biasing force produced by the spring. The amount of current supplied to the solenoid to energize it is regulated by a current controller, and the area opened by the valve body or valve opening area takes on a value proportional to the amount of energizing current supplied.
Accidents can occur in which the current controller for the electromagnetic valve and the solenoid are severed or disconnected from each other or short circuited. If the two are severed, the solenoid can no longer be energized and the valve body will be forced to close the valve due to the biasing force of the spring. In the event of a short circuit, on the other hand, the maximum amount of energizing current will flow through the solenoid so that the valve body will assume a position that maximizes the valve opening area. Malfunctions of this type have a deleterious effect upon engine idling. In particular, the aforementioned short circuit results in an excessive amount of supplementary air for control of idling operation, thereby causing the idling rotational speed of the engine to rise abnormally.